diff --git a/components/servo_arc/lib.rs b/components/servo_arc/lib.rs
index ad4489c10bc..bd6b5289504 100644
--- a/components/servo_arc/lib.rs
+++ b/components/servo_arc/lib.rs
@@ -485,6 +485,14 @@ impl<T: ?Sized> Arc<T> {
         }
     }
 
+    /// Whether or not the `Arc` is a static reference.
+    #[inline]
+    pub fn is_static(&self) -> bool {
+        // Using a relaxed ordering to check for STATIC_REFCOUNT is safe, since
+        // `count` never changes between STATIC_REFCOUNT and other values.
+        self.inner().count.load(Relaxed) == STATIC_REFCOUNT
+    }
+
     /// Whether or not the `Arc` is uniquely owned (is the refcount 1?) and not
     /// a static reference.
     #[inline]
@@ -501,10 +509,7 @@ impl<T: ?Sized> Drop for Arc<T> {
     fn drop(&mut self) {
         // NOTE(emilio): If you change anything here, make sure that the
         // implementation in layout/style/ServoStyleConstsInlines.h matches!
-        //
-        // Using a relaxed ordering to check for STATIC_REFCOUNT is safe, since
-        // `count` never changes between STATIC_REFCOUNT and other values.
-        if self.inner().count.load(Relaxed) == STATIC_REFCOUNT {
+        if self.is_static() {
             return;
         }
 
diff --git a/components/style/stylesheets/stylesheet.rs b/components/style/stylesheets/stylesheet.rs
index 15c60402be4..f5194d7d443 100644
--- a/components/style/stylesheets/stylesheet.rs
+++ b/components/style/stylesheets/stylesheet.rs
@@ -124,6 +124,7 @@ impl StylesheetContents {
         url_data: UrlExtraData,
         quirks_mode: QuirksMode,
     ) -> Self {
+        debug_assert!(rules.is_static());
         Self {
             rules,
             origin,
@@ -144,6 +145,9 @@ impl StylesheetContents {
     /// Measure heap usage.
     #[cfg(feature = "gecko")]
     pub fn size_of(&self, guard: &SharedRwLockReadGuard, ops: &mut MallocSizeOfOps) -> usize {
+        if self.rules.is_static() {
+            return 0;
+        }
         // Measurement of other fields may be added later.
         self.rules.unconditional_shallow_size_of(ops) +
             self.rules.read_with(guard).size_of(guard, ops)